A) Field of the Invention
The present invention relates to a portable electronic apparatus having a communication device with permanent magnets and a direction (azimuth) measuring device, to a magnetic sensor unit suitable for the apparatus, and to a direction measuring method for the apparatus.
B) Description of the Related Art
A magnetic sensor unit is known which detects geomagnetism and measures a direction. Recent studies are directed to adding a navigation function to a portable electronic apparatus typically a portable phone having the communication device and the magnetic sensor unit capable of detecting geomagnetism, the communication device including a speaker, a microphone, a transceiver circuit, a display device and the like.
The communication device including a speaker, a microphone, a display device and the like has permanent magnets. The magnetic sensor unit outputs a signal corresponding to the synthesized magnetic field of geomagnetism and a magnetic field of permanent magnets. There arises therefore a problem that the direction determined from the signal output from the magnetic sensor unit is not precise. The magnetic field of a permanent magnet changes with the temperature of the magnet. If the signal of the magnetic sensor unit is corrected only by the influence of the magnetic field of the magnet detected at one temperature on the signal of the magnetic sensor, and the direction is determined from the corrected signal, the determined direction is not correct when the temperature of the magnet changes.